Evolution of the electronic structure in open-shell donor-acceptor organic semiconductors
Zhongxin Chen, Wenqiang Li, Md Abdus Sabuj, Yuan Li, Weiya Zhu, Miao Zeng, Chandra Shekar Sarap, Md Masrul Huda, Xianfeng Qiao, Xiaobin Peng, Dongge Ma, Yuguang Ma, Neeraj Rai, Fei Huang
Abstract
Most organic semiconductors have closed-shell electronic structures, however, studies have revealed open-shell character emanating from design paradigms such as narrowing the bandgap and controlling the quinoidal-aromatic resonance of the π-system. A fundamental challenge is understanding and identifying the molecular and electronic basis for the transition from a closed- to open-shell electronic structure and connecting the physicochemical properties with (opto)electronic functionality. Here, we report donor-acceptor organic semiconductors comprised of diketopyrrolopyrrole and naphthobisthiadiazole acceptors and various electron-rich donors commonly utilized in constructing high-performance organic semiconductors. Nuclear magnetic resonance, electron spin resonance, magnetic susceptibility measurements, single-crystal X-ray studies, and computational investigations connect the bandgap, π-extension, structural, and electronic features with the emergence of various degrees of diradical character. This work systematically demonstrates the widespread diradical character in the classical donor-acceptor organic semiconductors and provides distinctive insights into their ground state structure-property relationship.